Is cystic medionecrosis the cause of dissecting aortic aneurysm?

Abstract

Over 4 decades have elapsed since Erdheim described the aortic lesion currently referred to as idiopathic cystic medionecrosis, cystic medionecrosis, or medionecrosis of the aorta. In 2 articles each based on a single case, he noted that the lesions were essentially noninflammatory and were not associated with alterations in the intima, adventitia, or vasa vasorum. He stressed the lack of a healing reaction, and the resultant impairment in strength which predisposes to aneurysmal dilatation and rupture. The terms as employed by Erdheim are considered in most textbooks of pathology as the chief predisposing cause for dissecting aneurysms, a fact which never was contended by Erdheim himself. On the contrary there is considerable doubt that cystic medionecrosis is the most frequent lesion encountered in dissecting aneurysm. The term 'cystic' is inappropriate since the lesions (structural voids in the media) are more 'cavitary' than cystic, while the term 'medionecrosis' is not justified because, as Erdheim himself admitted, necrosis is seldom seen, but is inferred as a result of depletion of the cellular elements of the media. While Erdheim employed the term idiopathic (right at that time) recent studies provided some insight into the pathogenesis (although most cases must still be categorized as idiopathic). Elastic tissue defects with interruption of one or more laminae of the media leaving microscopic voids, often multiple which become filled with ground substance. As a result of elastic tissue loss, muscle cells lose their normal parallel orientation. The result is precisely the type of lesion that Erdheim described, which he apparently regarded as the result of a primary increase in ground substance, but which he - a pathologist - had never declared to be responsible for the development of a dissecting aneurysm. A review of large series of dissecting aneurysms showed that the frequency of 'cystic medionecrosis' ranged from 0-83%, which makes a difference in the threshold of this diagnosis among pathologists more than likely. In reality, medial elastic tissue lesions of the 'mucoid cystic' type are not a common cause of these aneurysms. Such lesions are found most consistently associated with Marfan's syndrome (less than 3% of the cases) and in the rare aneurysms of the ascending aorta occurring in the absence of syphilis or atherosclerosis. It seems advisable to abandon the term idiopathic cystic medionecrosis in favor of a terminology which designates the defective component(s) of the vessel wall as either muscle or elastic tissue or both.